Getting the first reply from a motor took three nights.

Night 1: a USB-to-CAN adapter straight from the Mac. The bus flooded and the motor never answered. I assumed the motor was the problem.

Night 2: a Teensy 4.1 with cheap SN65HVD230 transceiver boards. All three boards failed the same way. When they were supposed to drive the bus, both CAN lines dropped to about 0 V, even on a board that had never been near the motor. It seems to have been a bad batch.

Night 3: a genuine Waveshare SN65HVD230 board. It passed the line test right away, and the RS02 answered on the first ping. It was the same motor from night 1, so the motor had been fine all along. After that it was quick: a 45° move, then the RS00 on the same bus, a full turn, and a speed run that held 315 rpm.

Video: Both motors spinning together on one bus

Lesson: test the transceiver on its own first. If it can't pull the lines apart when driving, nothing else matters.